Director Sarah Polley’s documentary Stories We Tell revolves around her parentage. Can I leave it at that, and tell you no more? I’d like every viewer to have a chance to experience the movie’s slow reveals, rather than have its mysteries summarized in a few neat declarative sentences. Suffice it to say, there are family secrets. At one point in the film, Polley tells her sister “I can’t figure out why I’m exposing us all in this way. It’s really embarrassing.”

But while the secret, which Polley herself didn’t know until 2006, is titillating, it’s not as intriguing as the style of the filmmaking, which leans more toward creative non-fiction than traditional documentary. Stories We Tell is blatantly sly, nudging the viewer to question everything they’re hearing and seeing. It’s also playfully meta—Polley’s considerable celebrity in Canada has an obvious impact on some of the secret-keepers—but without being mannered or precious. Yet despite this somewhat elastic structure, Polley renders her portrait of family love and identity in such a heartfelt, pure way that at the end, I had tears running down my face. As a narrative, Stories We Tell isn’t entirely trustworthy, but ultimately, it’s emotional content can absolutely be trusted.

The most obviously captivating member of the Polley clan is one we glimpse only in photographs and home movies—Diane, the actress mother who died of cancer when Polley was 11 and just starting her own acting career as the star of the popular Canadian television series Road to Avonlea. But the director herself, hovering on the sidelines, is equally seductive. You’ll likely fall for the mind behind this strange project, presuming you didn’t fall for Sarah Polley long ago, when she was the coolest girl in Hollywood, starring in movies like 1999’s Go or 2000’s The Claim or later, when she turned into the kind of formidable young woman who could successfully adapt Alice Munro for the screen (into Away From Her) before she turned 27.

In a recent video interview with journalist Anne Thompson, Polley referred to the “soap-opera-ish aspect” of the story she’s telling. Like a soap opera, Stories We Tell does feature a large “cast,” so many, in fact, that I lost track of some of their names. There are friends of Diane Polley, fellow stage actors, her husband Michael Polley (who was also an actor, before he had children to feed), some old lovers and all five of her children. These include two from Diane’s first marriage, Susy Buchan and John Buchan, and then the Polleys, Mark, Joanna and Sarah herself. They’re all there, to provide testimony as to what they believe, or believed, about the family unit. Home footage is featured throughout the production, although in some cases, the scenes seem so perfectly out of a movie that it’s hard to be sure what’s real.

The counterweight to that disorientation is the affection and good-humor between the family members, natural performers all. “I was being so real,” Michael Polley jokes when Sarah interrupts him and asks him to repeat something. “Is this a good angle for me?” asks John, posing hard. He goes on to challenge his little sister to explain what the movie is really about. “It’s about a lot of things,” Polley answers slowly. “Memory, and the way we tell the stories of our lives.” When he makes fun at her, she directs a mild expletive at him that speaks volumes about their intimacy. The name-calling can be meant in the moment because it will never be meant for more than a moment; this easy confidence of enduring love is what strong families have that others envy.

The large cast of characters is key to Polley’s goal of gathering the truth not as facts determine it, but as people feel it. The facts are almost an aside. As the youngest, and as a child raised without her mother from an early age, Sarah Polley had been subject to a sort of game of telephone, the mythology of her own history passed back and forth across her head by people who don’t know anything for sure, but have heard rumors. At least one of her key subjects, a man who holds a secret about Diane’s past, insists that no truth is to be found from assembling so many points of view about a family’s history. He thinks the story belongs only to the principals, he being one of them, and he and and Polley tussle (in emails read aloud by both) about the proper way to turn this into a film.

Meanwhile, her father Michael refers to the film in process a “theatrical exercise” and muses aloud about how editing — her editing — will reshape everyone’s version of the story. But Polley’s insistence on including them all creates a vivid portrait of the essence of a family, people who lived as a collective but carried away with them their individual perspectives and who, when they come together, tend to fight about the minutiae of their shared history. Why? Because it keeps alive that time when the stories were not being told, but being lived, when the “we,” the “us,” was happening in real time.

Polley returns repeatedly to a scene of her father reading aloud his version of the Polley family’s story of “us,” a document he wrote in a time of existential crisis. It is poetic and carries with it a feeling of the universal; as you listen to him read it, it seems natural that his daughter would become such a great story teller herself. But it’s also a studied document, carefully worked over, and undeniably, presents a best version of self. Polley displays the steely strength of a documentarian when she sits down with a camera in her father’s apartment, where he sits smoking — sadly, so sadly — and asks him what he said to her mother as she lay dying. Playing behind this scene is Timber Timbre’s dreamily evocative “Demon Host,” which incorporates some of the words from the old nursery rhyme “Here’s the church, here’s the steeple.”

Michael’s mask of the jovial bard is shaken and his eyes fill with tears. “What are you, some kind of sadistic interviewer,” he murmurs, lighting what might be his fortieth cigarette of the film. “You see what a vicious director you are.” She’s impressed him, going for the emotional jugular (in the sweetest of tones). Then he goes on to tell a story about the time she made him perform in one of her student films. In other words, he tells her a story about the time she used him in one of her other stories, and he’s fairly bursting with pride and paternal joy as he tells it. Polley has referred to her mother as unleashing a tsunami on them all, but in this magical moment, I came to think of the film as taking the shape of another natural disaster, a tornado, hovering, sweeping up all the pieces of the Polley family past and spinning them into the terrifying air. But after all that turmoil, this wise young director gently places them all back where they belong.

Mary Pols has been reviewing film and occasionally books for TIME since 2009. She has degrees from Duke University, where she studied art history, and the University of California Berkeley’s School of Journalism. She is the author of a memoir about untraditional parenthood. It was made into a short-lived television comedy where everything turned out traditionally.

Accidentally on Purpose: The True Tale of a Happy Single Mother is available for nearly nothing at various online bookstores and from boxes in Pols' barn.